As a tire pressure monitoring system (hereinafter referred to as the TPMS), there is a direct TPMS. The direct TPMS is configured so that a transmitter having a pressure sensor or other sensor is directly attached to a tire wheel. Further, an antenna and a receiver are attached to a vehicle. When a detection signal outputted from the sensor is transmitted by the transmitter, the receiver receives the detection signal through the antenna to perform tire pressure detection.
When the above-mentioned direct TPMS is used, it is necessary to determine whether the transmitted data is for a subject vehicle and which tire wheel the transmitter is attached to. Therefore, the data transmitted from the transmitter includes ID information for determination as to whether the transmitted data is for the subject vehicle or for a different vehicle and which tire wheel the transmitter is attached to.
In order to identify the position of the transmitter from the ID information included in the transmitted data, it is necessary to associate the ID information of each transmitter with the position of each tire wheel and preregister the association in the receiver. For example, the ID information of a transmitter of the subject vehicle is registered by reading a barcode on the transmitter with a barcode reader and registering an ID through the barcode reader. However, the use of this method requires a barcode reader and increases the man-hours necessary for reading the barcode on the transmitter attached to each tire wheel.
The relationship between the ID information of a transmitter and the position of a tire wheel needs to be re-registered in the receiver when, for example, tire rotation is performed or tires are replaced with snow tires. This inhibits a user from freely replacing the tires. Therefore, there is a need for a system that automatically registers the ID information. In this respect, a technology for automatically registering the ID information is proposed, for example, in Patent Literature 1.
More specifically, a device described in Patent Literature 1 receives an acceleration detection signal outputted from an acceleration sensor attached to a transmitter on a tire wheel, uses the received acceleration detection signal to detect that the tire wheel is at a predetermined rotational position (rotation angle), and then causes the tire wheel to transmit a frame. When a registration procedure is accordingly performed by the user, a tire wheel velocity sensor detects the passage of teeth of a gear rotating in coordination with the tire wheel, and identifies the position of the tire wheel based on the variation in the positions of the teeth at a time point at which the frame is received.
The tire wheel position may alternatively be identified by entering an ID registration mode for registering the ID information of a transmitter, transmitting predetermined radio waves from a vehicle body to the transmitter by using a triggering device, and causing the transmitter to transmit response data to a receiver in synchronism with the radio waves. Another alternative method of identifying the tire wheel position is to attach a two-axis acceleration sensor to each transmitter, identify left and right tire wheels based on a detection signal from the two-axis acceleration sensor, and identify front and rear tire wheels based on reception strength at which a frame from each transmitter is received by the receiver. Still another alternative is to dispose an antenna in the vicinity of each tire wheel, measure the strength (RSSI) of received radio waves when the antenna receives a frame, and register a great strength value as the ID information of a tire wheel in the vicinity of the antenna.